Then going in Jack's direction, finding giant (4)
I believe the answer is:
ogre
'giant' is the definition.
(I know this)
'then going in jack's direction' is the wordplay.
'then' becomes 'ergo' (therefore).
'going in jack's direction' is a reversal indicator.
'ergo' in reverse letter order is 'OGRE'.
'finding' is the link.
(Other definitions for ogre that I've seen before include "Giant who eats people" , "Giant of folklore who liked to eat humans" , "Cruel and wicked person" , "Fierce giant" , "Brute" .)